CI-1658: Remove deprecated ioutil package

Implement go-staticcheck suggestions.

Replaces ioutil with new functions in the os package.
Each function in the os package is a direct replacement for the
previously used functions in the ioutil package.

For more context see these:
- go-critic/go-critic#1019
- golang/go#42026

apis/vault/v1alpha1/secretsinjector_webhook_test.go

@@ -2,7 +2,7 @@ package v1alpha1
 
 import (
 	"fmt"
-	"io/ioutil"
+	"os"
 	"time"
 
 	corev1 "k8s.io/api/core/v1"
@@ -15,7 +15,7 @@ import (
 )
 
 func mustPodFixture(path string) *corev1.Pod {
-	podFixtureYAML, _ := ioutil.ReadFile(path)
+	podFixtureYAML, _ := os.ReadFile(path)
 	decoder := scheme.Codecs.UniversalDeserializer()
 	obj, _, _ := decoder.Decode(podFixtureYAML, nil, nil)
 	return obj.(*corev1.Pod)

apis/workloads/v1alpha1/console_authorisation_webhook_test.go

@@ -1,8 +1,8 @@
 package v1alpha1
 
 import (
-	"io/ioutil"
 	"net/http"
+	"os"
 
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
@@ -14,7 +14,7 @@ import (
 func mustConsoleAuthorisationFixture(path string) *ConsoleAuthorisation {
 	consoleAuthorisation := &ConsoleAuthorisation{}
 
-	consoleAuthorisationFixtureYAML, _ := ioutil.ReadFile(path)
+	consoleAuthorisationFixtureYAML, _ := os.ReadFile(path)
 
 	decoder := serializer.NewCodecFactory(runtime.NewScheme()).UniversalDeserializer()
 	if err := runtime.DecodeInto(decoder, consoleAuthorisationFixtureYAML, consoleAuthorisation); err != nil {

cmd/theatre-secrets/main.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	execpkg "os/exec"
@@ -243,7 +242,7 @@ func mainError(ctx context.Context, command string) (err error) {
 			path := file.filesystemPath
 			if path == "" {
 				// generate file path prefixed by key
-				tempFilePath, err := ioutil.TempFile("", fmt.Sprintf("%s-*", key))
+				tempFilePath, err := os.CreateTemp("", fmt.Sprintf("%s-*", key))
 				if err != nil {
 					return errors.Wrap(err, fmt.Sprintf("failed to write temporary file for key %s", key))
 				}
@@ -264,7 +263,7 @@ func mainError(ctx context.Context, command string) (err error) {
 			)
 
 			// write file with value of envMap[key]
-			if err := ioutil.WriteFile(path, []byte(secretEnv[file.vaultKey]), 0600); err != nil {
+			if err := os.WriteFile(path, []byte(secretEnv[file.vaultKey]), 0600); err != nil {
 				return errors.Wrap(err,
 					fmt.Sprintf("failed to write file with key %s to path %s", key, path))
 			}
@@ -304,7 +303,7 @@ func mainError(ctx context.Context, command string) (err error) {
 // in cluster auth but falling back to other detection methods if that fails.
 func getKubernetesToken(tokenFileOverride string) (string, error) {
 	if tokenFileOverride != "" {
-		tokenBytes, err := ioutil.ReadFile(tokenFileOverride)
+		tokenBytes, err := os.ReadFile(tokenFileOverride)
 
 		return string(tokenBytes), errors.Wrap(err, "failed to read kubernetes token file")
 	}
@@ -470,7 +469,7 @@ type Config struct {
 func loadConfigFromFile(configFile string) (Config, error) {
 	var cfg Config
 
-	yamlContent, err := ioutil.ReadFile(configFile)
+	yamlContent, err := os.ReadFile(configFile)
 	if err != nil {
 		return cfg, errors.Wrap(err, "failed to open config file")
 	}

cmd/vault-manager/acceptance/acceptance.go

@@ -5,8 +5,8 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
+	"os"
 	"strings"
 	"time"
 
@@ -46,15 +46,17 @@ func (r *Runner) Name() string {
 //
 // It does several things:
 //
-// - Mounts a kv2 secrets engine at secret/
-// - Creates a Kubernetes auth backend mounted at auth/kubernetes
-// - Configures the Kubernetes backend to authenticate against the currently detected
-//   Kubernetes API server (the current cluster, if run from within)
-// - For all successful Kubernetes logins, the user is assigned a token that maps to a
-//   cluster-reader policy, which permits reading of secrets from:
+//   - Mounts a kv2 secrets engine at secret/
 //
-//   secret/data/kubernetes/{namespace}/{service-account-name}/*
+//   - Creates a Kubernetes auth backend mounted at auth/kubernetes
 //
+//   - Configures the Kubernetes backend to authenticate against the currently detected
+//     Kubernetes API server (the current cluster, if run from within)
+//
+//   - For all successful Kubernetes logins, the user is assigned a token that maps to a
+//     cluster-reader policy, which permits reading of secrets from:
+//
+//     secret/data/kubernetes/{namespace}/{service-account-name}/*
 func (r *Runner) Prepare(logger kitlog.Logger, config *rest.Config) error {
 	cfg := api.DefaultConfig()
 	cfg.Address = "http://localhost:8200"
@@ -110,7 +112,7 @@ func (r *Runner) Prepare(logger kitlog.Logger, config *rest.Config) error {
 	var ca []byte = config.CAData
 
 	if len(ca) == 0 {
-		ca, err = ioutil.ReadFile(config.CAFile)
+		ca, err = os.ReadFile(config.CAFile)
 		if err != nil {
 			return errors.Wrap(err, "could not parse certificate for kubernetes")
 		}